Hi Swathi,
While I can understand the problem you are in, I would still say that you keep quite in this situation and act in consensus rather that being unanimous, as some others have said before.
Don't ever voice your worries and concerns bluntly as it has every chance of getting backfired upon you, especially because you are pointing fingers towards the Dept. Head.
Please take steps professionally rather than being emotional. We all have faced similar situations in some form or the other, but with tact and patience overcame them. That is how, we learnt to cope up with Corporate politics.
Remember, that end of the year your appraisals would probably be in the hands of this person or his/her immediate delegate and it may have a devastating impact which could be detrimental for your career in the organisation you are in.
So please take steps professionally, and please document whatever you do and nothing verbally.
Regards,
Probhat